Color picture tube apparatus

Abstract: In a color picture tube apparatus having a first auxiliary deflecting means (GD1, GD2) for deflecting a single electron beam, emitted from a cathode (K), in a direction to separate from the tube axis (Z) in synchronism with switching among a plurality of video signals supplied to an electron gun, and splitting the single electron beam substantially into a plurality of beam segments, and a second auxiliary deflecting means, disposed between the first auxiliary deflecting means (GD1, GD2) and a main deflecting unit, for deflecting the plurality of beam segments in a direction to come close to the tube axis, the first auxiliary deflecting means (GD1, GD2) is constituted by an electrostatic deflecting lens provided to an accelerating electrode system between a control electrode (G1) and a focusing electrode (G4) of the electron gun, and the second auxiliary deflecting means is constituted by a main electron lens (ML) of the electron gun for finally focusing the electron beam segments on a phosphor screen. Accordingly, the entire length of the picture tube can be shortened, and the auxiliary deflecting power can be reduced as well as the manufacturing cost.

Description: The present invention relates to a color picture tube apparatus and, more particularly, to a color picture tube apparatus for displaying an image by time-dividing a single electron beam substantially into a plurality of beams. Generally, a color picture tube apparatus incorporates an electron gun assembly for emitting three electron beams. The three electron beams emitted from the electron gun assembly are deflected by a magnetic field generated by a deflecting unit and scan a phosphor screen opposing the electron gun assembly through a shadow mask in the horizontal and vertical directions, thereby displaying a color image on the screen. In contrast to this color picture tube apparatus, Jpn. Pat. Appln. KOKAI Publication No. 61-263030 discloses a color picture tube apparatus in which a single electron beam is emitted from a cathode and is time-divided substantially into three electron beams, thereby displaying an image. More specifically, as shown in FIG. 1, this color picture tube apparatus has an electron gun comprising one cathode K for emitting a single electron beam 1, first, second, third, fourth, and fifth grids (only a fourth grid G4 is shown in FIG. 1) which are arranged between the cathode K and a phosphor screen 2 and control, accelerate, and focus the electron beam or electron beam segment(s) emitted from the cathode K, and a convergence electrode C. In this apparatus, the fourth grid G4 is constituted by two electrodes opposing each other as the first auxiliary deflecting means. The single electron beam 1 from the cathode K is electrostatically deflected by the first auxiliary deflecting means in three steps in a direction to separate from a tube axis Z, so that it is split into three beam segments. The convergence electrode C is constituted by a pair of central electrodes C1 serving as the second auxiliary deflecting means and a pair of two side electrodes C2 arranged on the two sides of the central electrodes C1. Each electron beam segment deflected by the first auxiliary deflecting means in the direction to separate from the tube axis is electrostatically deflected by the convergence electrode C in a direction to come close to the tube axis Z. Referring to FIG. 1, reference numeral 5 denotes a main deflecting unit for deflecting the three beam segments; 6, a deflection center plane of the main deflecting unit 5; 7, a shadow mask; and 8, a three-color video signal switch for switching among red, green, and blue video signals. According to this color picture tube apparatus, since the gap among the electron beam segments that are incident on the deflection center plane of the deflecting unit can be made small, a high-resolution, high-convergence color image can be displayed. This color picture tube apparatus, however, has problems as follows. Namely, two auxiliary deflecting means are required for auxiliary deflection of the single electron beam emitted from the cathode. This increases the entire length of the picture tube and the deflecting power required for auxiliary deflection. Also, the manufacturing cost increases. As described above, a color picture tube apparatus which time-divides a single electron beam substantially into three electron beam segments is conventionally known. However, since this color picture tube apparatus requires two auxiliary deflecting means for auxiliary deflection of the single deflection beam, the entire length of the picture tube increases, and the deflecting power required for auxiliary deflection also increases. Again, the manufacturing cost rises. Both US-A-2 927 236 and EP-A-0 198 494 disclose such color cathode ray tubes described above. In other words, a single electron beam is deflected by first and second deflecting means and focused by separate focusing means. It is an object of the present invention to provide a color picture tube apparatus for dividing a single electron beam substantially into three electron beam segments by two auxiliary deflecting means, in which the entire length of the picture tube, the deflecting power required for auxiliary deflection, and the manufacturing cost can all be reduced. According to the present invention, there is provided a color picture tube apparatus as set out in the claims comprising means for generating first, second and third video signals; means for generating a single electron beam; applying means for continuously and alternately supplying said first, second and third video signals to said single electron beam generating means to modulate said single electron beam; control means for forming a crossover by controlling said electron beam, auxiliary deflecting means for accelerating said single electron beam from said crossover, said auxiliary deflecting means splitting said accelerated single electron beam into first, second and third electron beam segments respectively corresponding to said first, second and third video signals, said auxiliary deflecting means splitting said accelerated single electron beam by performing electrostatic auxiliary deflection of said accelerated single electron beam in synchronism with application of said first, second and third video signals to said single electron beam generating means; a shadow mask ; light ray generating means for generating light rays in response to incidence of said first, second and third electron beam segments; an electrostatic lens for focusing said first, second and third electron beam segments from said auxiliary deflecting means on said light ray generating means; and main deflecting means for deflecting said first, second and third electron beam segments to scan said light ray generating means with said electron beam segments in horizontal and vertical directions; wherein said auxiliary deflection means are located sufficiently close to said crossover to permit said electrostatic lens to converge said first, second and third electron beam segments and focus the respective electron beam segments onto said light ray generating means. As described above, when the (first) auxiliary deflecting means is provided and the main electrostatic lens is utilized as a second auxiliary deflecting means, an additional second auxiliary deflecting means need not be particularly provided, and the entire length of the picture tube, the auxiliary deflecting power, and the manufacturing cost can all be reduced. When the first auxiliary deflecting means is constituted by the electrostatic deflecting lens provided to the accelerating electrode system between the control and focusing electrodes, since auxiliary deflection is performed in a region where the electron beam has a low speed, the auxiliary deflecting power can be decreased. Also, since first auxiliary deflection is performed near the crossover point of the electron beam, the second auxiliary deflecting means is constituted by the main electrostatic lens, thus a plurality of split beams can be focused and converged simultaneously. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a diagram for explaining the operation of a conventional color picture tube apparatus; FIG. 2 is a sectional view schematically showing the structure of an electron gun according to an embodiment of the present invention; FIG. 3 is a sectional view schematically showing the structure of a color picture tube apparatus according to the embodiment of the present invention; FIG. 4 is a diagram for explaining the operation of this color picture tube apparatus; and FIGS. 5A and 5B are diagrams for explaining focusing and convergence of three electron beam segments by the electrostatic lens of the color picture tube apparatus. The preferred embodiment of a color picture tube apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 3 shows the structure of the color picture tube apparatus according to the embodiment of the present invention. This color picture tube apparatus has an envelope constituted by a panel 10 and a funnel 11 integrally bonded to the panel 10. A phosphor screen 12 comprising three-color stripe phosphor layers that emit blue, green, and red light is formed on the inner surface of the panel 10. A shadow mask 13 formed with a large number of electron beam passage openings is arranged inside the phosphor screen 12 to oppose it. An electron gun 15 is sealed in a neck 14 of the funnel 11. In the funnel 11, an inner surface conductive film 17 is formed to extend from the inner surface of a large-diameter portion 16 to an inner surface adjacent to the neck 14 of the funnel 11. This inner surface conductive film 17 is connected to an anode terminal 18 provided on the side surface of the large-diameter portion 16 of the funnel 11. A main deflecting unit 19 is adhered on the outer side of the boundary between the large-diameter portion 16 and the neck 14 of the funnel 11. As shown in FIG. 2, the electron gun 15 has a cathode K for emitting a single electron beam, a heater H for heating the cathode K, and first to sixth grids G1 to G6 for controlling, accelerating, and focusing the electron beam or electron beam segments from the cathode K. The cathode K, the heater H, and the first to sixth grids G1 to G6 are integrally fixed with a pair of insulating supports (not shown). The first and second grids G1 and G2 are constituted by flat electrodes closely opposing each other. Comparatively small circular openings are formed in the plate surfaces of the grids G1 and G2, respectively, and pass the electron beam therethrough. The third grid G3 is also constituted by a flat electrode. A circular opening larger than that of the second grid G2 is formed in the third grid G3 to pass the electron beam segments therethrough. The fourth, fifth, and sixth grids G4, G5, and G6 are constituted by cylindrical electrodes through which the electron beam segments pass and which are arranged at predetermined gaps therebetween. In this color picture tube apparatus, an auxiliary deflecting means comprising a pair of deflecting electrodes GD1 and GD2, i.e., the first auxiliary deflecting means, is arranged in an accelerating electrode system between the second and third grids G2 and G3. The pair of deflecting electrodes GD1 and GD2 are arranged to oppose each other in the horizontal direction, e.g., in the X-axis direction through a tube axis Z coinciding with the axis of the electron gun, such that the gap between the deflecting electrodes GD1 and GD2 is larger at the third grid GD3 side than at the second grid GD2 side. The deflecting electrodes GD1 and GD2 are fixed to a pair of insulating supports together with the respective electrodes of the electron gun. Voltages as defined below are applied to the respective electrodes of the electron gun. More specifically, the cathode K is kept at a cut-off electrode of about 150 V. Three color video signals are sequentially supplied to the cathode K through a three-color video signal switch 8 at a predetermined period. The first grid G1 is applied with the ground potential. The second and third grids G2 and G3 are applied with a voltage of about 700 V. The fourth grid G4 is applied with a voltage of about 15 kV. The fifth grid G5 is applied with the ground potential. The sixth grid G6 is applied with a voltage of about 15 kV, which is the same as the voltage applied to the fourth grid G4. The first auxiliary deflecting means is applied with a voltage of about 700 V so that a potential difference of about several tens to several hundreds V is set between the pair of deflecting electrodes GD1 and GD2. As a result of this voltage application, generation of the single electron beam from the cathode K is controlled by the first and second grids G1 and G2. The emitted electron beam forms a crossover CO in the vicinity of the second grid G2, and is incident on an electrostatic deflecting lens formed by the pair of deflecting electrodes GD1 and GD2 of the first auxiliary deflecting means, so that it is split into three electron beam segments. Thereafter, the three electron beam segments pass through the third grid G3, and are incident on a main electrostatic lens ML formed by the fourth, fifth, and sixth grids G4, G5, and G6, so that they are finally focused on the phosphor screen. In this case, when the voltage applied to the pair of deflecting electrodes GD1 and GD2 of the first auxiliary deflecting means is changed in three steps in synchronism with the three color video signals supplied to the cathode K, the first auxiliary deflecting means deflects the single electron beam, which is incident thereon through the crossover CO, in three steps in the horizontal direction to separate from the tube axis, thereby splitting the single electron beam substantially into three electron beam segments 21B, 21G, and 21R that are modulated by the three color video signals. Of the three electron beam segments 21B, 21G, and 21R, the center electron beam segment 21G which is not deflected is incident on the central portion of the main electrostatic lens ML formed by the fourth, fifth, and sixth grids G4, G5, and G6, and reaches the central portion of the phosphor screen through the central portion of the main electrostatic lens ML. The side electron beam segments 21B and 21R, which are deflected by the first auxiliary deflecting means, are incident on the peripheral portion of the main electrostatic lens ML, and are deflected by the lens operation of the main electrostatic lens ML in the horizontal direction such that the central axes of the electron beam segments 21B and 21R come close to the tube axis Z. More specifically, in this electron gun, the main electrostatic lens ML formed by the fourth, fifth, and sixth grids G4, G5, and G6 has a function of finally focusing the electron beam segments on the central portion of the phosphor screen, and a function as the second auxiliary deflecting means of converging the three electron beam segments 21B, 21G, and 21R, obtained by three-step deflection of the first auxiliary deflecting means on the phosphor screen. The three electron beam segments 21B, 21G, and 21R, which are deflected by the first auxiliary deflecting means in a direction to separate from the tube axis, are finally focused and converged on the central portion of the phosphor screen by the operations of the main electrostatic lens ML. The third grid G3 prevents a quadrupole lens, that distorts an electron beam, from being formed between the pair of deflecting electrodes GD1 and GD2 of the first auxiliary deflecting means and the high-potential fourth grid G4. Therefore, when the first auxiliary deflecting means is provided to the electron gun in the manner as described above, as shown in FIG. 4, the single electron beam emitted from the cathode K is deflected by an electrostatic deflecting lens ED, formed by the first auxiliary deflecting means, in the horizontal direction to separate from the tube axis Z, and is split substantially into three electron beam segments 21B, 21G, and 21R modulated by the three color video signals. The three electron beam segments 21B, 21G, and 21R are focused and deflected by the main electrostatic lens ML in the horizontal direction to be close to the tube axis Z. Thereafter, the three electron beam segments 21B, 21G, and 21R are deflected by a magnetic field generated by the main deflecting unit 19. The phosphor screen 12 is scanned in the horizontal and vertical directions by the three deflected electron beam segments through the shadow mask 13. In the electron gun having the above structure, a second auxiliary deflecting means is not particularly needed in addition to the first auxiliary deflecting means for deflecting the three electron beam segments 21B, 21G and 21R, that are deflected in the direction to separate from the tube axis, in a direction to come close to the tube axis, and thus a space for providing the second auxiliary deflecting means is not necessary. Accordingly, the entire length of the color picture tube apparatus can be shortened. When compared to the apparatus shown in FIG. 1 which has a particular second auxiliary deflecting means, in the apparatus shown in FIG. 4, an increase in deflecting power can be avoided, and the manufacturing cost of the color picture tube apparatus can be decreased. When the lens operation of the main electrostatic lens ML of the electron gun is utilized as the second auxiliary deflecting means, as described above, focusing and convergence of the three electron beam segments 21B, 21G, and 21R are sometimes difficult to perform simultaneously in an optimum state. More specifically, in FIG. 5A, after the single electron beam emitted from the cathode K forms a crossover CO, it is deflected by the electrostatic deflecting lens ED, formed by the first auxiliary deflecting means, in a direction to separate from the tube axis Z so that it is split substantially into the three electron beam segments 21B, 21G, and 21R. The three electron beam segments 21B, 21G, and 21R are then focused and converged by the main electrostatic lens ML. In this structure, an object point A seen from the main electrostatic lens ML and related to focusing of the respective electron beam segments 21B, 21G, and 21R coincides with the position of the crossover CO. Meanwhile, an object point B related to convergence coincides with the position of the electrostatic deflecting lens ED formed by the first auxiliary deflecting means. As the object point related to focusing and the object point related to convergence do not coincide, focusing and convergence cannot be performed simultaneously. For example, if the main electrostatic lens ML has a power appropriate for convergence of the three electron beam segments 21B, 21G, and 21R, the three electron beam segments 21B, 21G, and 21R are over-focused. On the other hand, if the main electrostatic lens ML has a power appropriate for focusing of the three electron beam segments 21B, 21G, and 21R, the three electron beam segments 21B, 21G, and 21R are insufficiently converged. However, as in this color picture tube apparatus, assume that the first auxiliary deflecting means is provided in the vicinity of the second grid G2 serving as the accelerating electrode, i.e., is provided to the accelerating electrode system arranged between the first grid G1 serving as the control electrode and the fourth grid G4 serving as the focusing electrode. Then, as shown in FIG. 5B, the object point A seen from the main electrostatic lens ML and related to focusing of the three electron beam segments 21B, 21G, and 21R, i.e., the position of the crossover CO, and the object point B related to convergence, i.e., the position of the electrostatic deflecting lens ED formed by the first auxiliary deflecting means, are sufficiently close to each other. Thus, focusing and convergence of the three electron beam segments 21B, 21G, and 21R can be simultaneously performed in an optimum state. In this case, even if the object point A related to focusing and the object point B related to convergence do not strictly coincide with each other, since the error of the uncoincidence is sufficiently small, it can be adjusted by a beam track adjusting magnet which is conventionally used in an ordinary color picture tube apparatus. Concerning convergence of the three electron beam segments 21B, 21G, and 21R, Jpn. Pat. Appln. KOKAI Publication No. 61-265989 discloses a technique in which the electron gun is fabricated as an electron gun that emits three electron beams parallel to each other and the convergence error on the phosphor screen is corrected by controlling the phases of the three color video signals. When the present invention is combined with this technique, a color picture tube apparatus having the same effect can be obtained. In this case, the three electron beams need not be converged completely on the phosphor screen. It suffices if at least after the three electron beam segments are converged by the main electrostatic lens ML, they are deflected parallel to each other or in a direction to be close to the axis of the electron gun. As described above, when the first auxiliary deflecting means for deflecting the electron beam, emitted from the cathode K, in three steps in a direction to separate from the tube axis, and splitting the single electron beam substantially into three electron beam segments, is arranged in the accelerating electrode system arranged between the control and focusing electrodes of the electron gun 15, even if the main electrostatic lens ML of the electron gun 15 is used as the second auxiliary deflecting means for deflecting the three electron beam segments, deflected in the direction to separate from the tube axis, in a direction to come close to the tube axis, focusing and convergence of the three electron beam segments can be simultaneously performed in an optimum state. In addition, since the accelerating electrode system portion is maintained at a comparatively low potential of about 1 kV at maximum, power required for auxiliary deflection of the electron beam can be decreased. In the above embodiment, an electron gun in which the main electrostatic lens constitutes a uni-potential type electrostatic lens has been described. The present invention can also be applied of other electron guns. In the above embodiment, the three electron beam segments obtained by the first and second auxiliary deflecting means are arranged in a line. However, the present invention can also be applied to a case wherein the three electron beam segments obtained by these auxiliary deflecting means are arranged in a delta shape. In the above embodiment, an electron beam is deflected by the first auxiliary deflecting means in three steps to substantially obtain three electron beam segments. Deflection performed by the first auxiliary deflecting means is not limited to deflection in three steps. The present invention can also be applied to a case wherein an electron beam is deflected in a plurality of steps to obtain substantially a plurality of beams. In the above embodiments, a color picture tube apparatus having one electron gun for one phosphor screen has been described. The present invention can also be applied to each electron gun of a color picture tube apparatus as disclosed in Jpn. UM Appln. KOKAI Publication No. 47-9349, Jpn. UM Appln. KOKOKU Publication No. 39-25641, Jpn. Pat. Appln. KOKOKU Publication No. 42-9349, and the like, wherein one phosphor screen is scanned with electron beams emitted from a plurality of electron guns by being divided into a plurality of regions. In a color picture tube apparatus having a first auxiliary deflecting means for deflecting a single electron beam, emitted from a cathode, in a direction to separate from the tube axis in synchronism with switching among a plurality of video signals supplied to an electron gun, and splitting the single electron beam substantially into a plurality of beam segments, and a second auxiliary deflecting means, disposed between the first auxiliary deflecting means and a main deflecting unit, for deflecting the plurality of beam segments in a direction to come close to the tube axis, when the first auxiliary deflecting means is constituted by an electrostatic deflecting lens provided to the accelerating electrode system between the control and focusing electrodes of the electron gun, and the second auxiliary deflecting means is constituted by a main electrostatic lens of the electron gun for finally focusing the electron beam segments on a phosphor screen, a second auxiliary deflecting means is not particularly required. Therefore, the entire length of the picture tube, the auxiliary deflecting power, and the manufacturing cost can all be decreased. Since the first auxiliary deflecting means performs auxiliary deflection at a region where the electron beam has a low speed as the electrostatic deflecting lens provided to the accelerating electrode system portion between the control and focusing electrodes, the auxiliary deflecting power can be reduced. Since first auxiliary deflection is performed near the crossover point of the electron beam, even if the second auxiliary deflecting means is constituted by the main electrostatic lens, a plurality of beam segments can be simultaneously focused and converged.

Claims: A color picture tube apparatus comprising: means (R, G, B) for generating first, second, and third video signals; means (K) for generating a single electron beam; applying means (8) for continuously and alternately supplying said first, second, and third video signals to said single electron beam generating means (K) to modulate said single electron beam; control means (G1, G2) for forming a crossover (CO) by controlling said electron beam; auxiliary deflecting means (GD1, GD2) for accelerating said single electron beam from said crossover (CO), said auxiliary deflecting means (GD1, GD2) splitting said accelerated single electron beam into first, second, and third electron beam segments respectively corresponding to said first, second, and third video signals, said auxiliary deflecting means (GD1, GD2) splitting said accelerated single electron beam by performing electrostatic auxiliary deflection of said accelerated single electron beam in synchronism with application of said first, second and third video signals to said single electron beam generating means (K) ; a shadow mask (13); light ray generating means (12) for generating light rays in response to incidence of said first, second, and third electron beam segments; an electrostatic lens (ML) for focusing said first, second, and third electron beam segments from said auxiliary deflecting means (GD1, GD2) on said light ray generating means (12); and main deflecting means (19) for deflecting said first, second, and third electron beam segments to scan said light ray generating means (12) with said electron beam segments in horizontal and vertical directions, characterized in that said auxiliary deflection means (GD1, GD2) are located sufficiently close to said crossover to permit said electrostatic lens (ML) to converge said first, second and third electron beam segments and focus the respective electron beam segments onto said light ray generating means (12). An apparatus according to claim 1, characterized in that said control means (G1, G2) includes first and second flat grid electrodes (G1, G2) each having an opening through which the single electron beam passes. An apparatus according to claim 2, characterized in that said auxiliary deflecting means (GD1, GD2) includes a pair of deflecting electrodes arranged between said second and third grid electrodes (G2, G3), said pair of deflecting electrodes (GD1, GD2) beeing arranged such that a gap therebetween widens along a traveling direction of the electron beam. An apparatus according to claim 1, characterized in that said electrostatic lens (ML) includes fourth, fifth, and sixth cylindrical grid electrodes (G4, G5, G6) through which the first, second, and third electron beam segments pass.

Inventors: KAMOHARA EIJI, NISHIMURA TAKASHI, SHIMOKOBE JIRO, KAMOHARA, EIJI, NISHIMURA, TAKASHI, SHIMOKOBE, JIRO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1994
Main classification: H01J31
IPC codes: H04N9, H01J31, H01J29